AlCl3-induced reactions of vinylcyclopropanes

Tetrahedron.

Vol. 34, pp. 993 to 996.

Pergamon Press 1978.

Al&INDUCED

Printed

inGreal

Britain

REACTIONS OF VINYLCYCLOPROPANES

DIMERIZATIONS

AND ADDITIONS

WITH REARRANGEMENT

J.YOVELL*, A. FELZENSTEIN and S. SAREL Department of Pharmaceutical Chemistry, The Hebrew University School of Pharmacy, Jerusalem, Israel (Received in UK 31 August 1977; Accepted

for publication 27 September 1977)

Abstract-l,l-ethano-2-methylenecyclohexane 5, 1,1,3,3diethano-2-methylenecyclohexane 6, a-cyclopropylstryene 7 and its p-chloro and p-methoxy derivatives 8 and 9, I-methyl-l-cyclopropylethylene 10, and I,l-dicyclopropyIethylene 11 were subjected to the action of AICl~~OEt24 in ether. Monomeric (1215) and dimeric (16, 17) homoallylic chlorides as well as some polymeric products were obtained. The mechanism and substituents effects are discussed and spectral data (IR, PMR and MS) of the products are presented.

The reactivity ,of vinylcyclopropane systems towards Lewis acids has been described in the context of cationic polymerization.‘-’ Ring retained structures (1) from 1,2addition and homoallylic (2) and cyclobutanic (3) structures from rearranging cyclopropylcarbinyl cations were found, and their distribution in various polymers correlated to electronic and steric properties of the substituents R, both in the starting monomers and in the intermediate cations.

- CHz -k 1 q

: - cHz-c-eH-cuzXu*-

&

?I!$ - kc1 -g56

-pm 12 13 '6 -I13 : R-R- CH2-cB2

-*5 12 : R-H

B cn -kcu,I 2 I CH2-CH3 q

The total conversions reported range from trace to over 90%, but complete material balance is ordinarily missing. In particular no reference is made to survival of monomeric species, whether in their initial form or as transformed products. This study describes formation of non-polymeric products from reactions of a number of vinylcyclopropane systems with aluminium chloride etherate (4) in etheral solution. 4 was intentionally chosen because of accessibility in pure form,’ with exclusion of HCl. The ether is bound to suppress polymerization by interacting both with the catalyst and with the growing chain.9 The reagent in this solvent consists of monomeric 1: lcomplex of AU, and diethylether.““” Equimolar quantities of a vinylcyclopropane compound and 4 were stirred at room temperature under nitrogen and strict anhydrous conditions until the organic reactant disappeared in the gas-chromatogram. No product showed in the chromatogram at this stage. The mixture was then poured into large excess of Na2C0, solution, and, after extraction and drying, the product was separated by preparative GLC. This study included the following substrates: 1,l - ethano - 2 - methylenecyclohexane (5), 1,1,3,3 - diethano - 2 - methylenecyclohexane (6), 1 - phenyl - 1 - cyclopropylethylene (7), 1 - (4 chlorophenyl) - 1 - cyclopropylethylene (8), 1 - (4 anisyl) - 1 - cyclopropylethylene (9), 1 - methyl - 1 cyclopropylethylene (10) and 1,l - dicyclopropylethylene (11). The results are shown in Scheme 1. The monomeric compounds (12-15) represent formal

2.82

-s14 15

-._ 7 14 : R=H

-,8 15

RN/

6

: R-Cl 9:IkOCH

R-

C"3-~-C"2&!H-M2-C"2~~ : -*16 17

-I10 11

-.11 17 : R=cyclopropyl

-.10 16 : R-ethyl

Scheme 1

l&conjugated additions of HCl across the vinylcyclopropane systems, while the dimeric ones (16, 17) are products of similar formal 1,5-additions coupled with non-rearranged 1,2_selfadditions of the olefins. The yields range from 60 to 76% calculated with reference to the consumption of the organic compound. Some polymeric material was formed in every case, but a white powdery polymer, undetectable by GLC, was the sole product from 9. The latter was devoid of cyclopropane signals in the NMR spectrum, and the integration ratio between the vinylic (cu r 5.0) and methoxy (co r 6.30) signals was 1: 8, suggesting that it contains a mixture of structures 2 and 3. The structures of the products were deduced from the following data: (1) Elemental analysis and MS establish the molecular formulas; (2) cyclopropane signals in the IR and NMR spectra are totally or partially eliminated 993

J.

994

YOVELL

(in 12, 14, 15 and 13, 16, 17, respectively); (3) triplet resonances at T 3.40-3.53 and quartet bands (triplet for 12 and 13) at T 2.40-2.68 represent the CHzCHXl groups, singlets at T 1.30-2.05 (exception in 17) show the vinylic Me, and the vinylic protons appear as triplets at T X07-5.68 (missing in 12 and 13); (4) absorption bands at 71%74Ocm-’ correspond to the C-Cl stretching vibrations; (5) mass-spectral fragmentations are in accord with the proposed structures (e.g. M-CH*CI and MCHzCHXl). The monomeric products are stereochemically pure cis compounds. It is a trivial case for 12 and 13, and follows from the NMR data for 14 and IS. The spectra of the latter are simple first order patterns (in contradistinction to those of 16 and 17, discussed below), and the chemical shifts of protons remote from the hetero atom are practically identical with those reported for analogous cisacetoxy- and trifluoroacetoxy-2-pentenes,” Chloroheptenes 16 and 17 are cis-trans mixtures, their NMR spectra being easily recognized as duplicates of the characteristic bands and splitting patterns superimposed on each other (Experimental). The isomeric ratio in 16 is ca 1: 4 (deduced from the integration figures), but the relative shifts of corresponding resonance in the two isomers are too small (0.03-0.09ppm) to allow configurational assignment. In 17 a ratio cis : tram = 7: 4 can be evaluated. The configurations were deduced by considering the relative population of the two limiting, most stable conformations of the vinylcyclopropane unit in the two isomers:‘3

ef ai.

of HCl is evidenced also by lack of co-catalysis with AKlp’5 (which should enhance polymerization) and by the non-occurrance of these products prior to hydrolysis.? Third, the hitherto unknown type of dimeric products (16 and 17),$ where the reaction is both regiospecific in the “head-to-tail” sense for the dimerizations and stereoselective in the rearrangement mode of the vinylcyclopropane systems. To rationalize these observations we propose the intermediacy of an organoaluminum species 19 which is polarized in opposite sense relative to the equilibrating dipolar structures (21) suggested for cationic polymerization.Z4” Compound 19 arises, presumably, from addition of the Al-Cl bond across the vinylcyclopropane system oia a pericyclic transition-state 18 (Scheme 2). The allylic carbon-metal bond in 19 is particularly suited for anionic addition to a polarized olefin,‘6,‘7leading to the dimeric species u), which, in turn, are not reactive enough for further chain-growth due to the loss of the allylic resonance participation. The same intermediate could exhibit cis-tram isomerization,§ which, in fact, occurs concurrently with dimerization.

v

v

cH3-c-at

c83 A-cH2d/cH2cI12c1Ae

s

114e-ciaoid

vi

H

l¶-huma

-c;

%&-LH2ca2c1

l7-trana-tronsoid

-m

Steric interaction of the cyclopropyl with the bulky chloroethyl group would diminish the probability of the cisoid arrangement in the trans as compared to the cis isomer. Consequently a relative diamagnetic shifts of the vinylic and CH&!HzCl protons resonances would be expected in the cis isomer, caused by the magnetic anisotropy of the ring, while, similarly, the other methylene and the methyl group should absorb at higher field in the frans isomer. Such a distribution of chemical shifts is, in fact, observed, and hence the assignment of the stereochemistry. The results presented here differ from the reported Lewis-acids-induced reactions of vinylcyclopropanes in three main respects: Fist, the very meaningful suppression of the polymerization process (except for 9), which is due to the reduction of the catalytic efficiency of anhydrous AICls by the coordination of ether molecules.14 Second, the formation of monomeric homoallylic chlorides (12-15) in absence of free HCl. The exclusion tin an experiment with NC1 added intentionally the product formation could be monitored by GLC simultaneously with the consumption of the substrate. *Note that these are not the known self-dimerization products of ailylaluminum~compounds.16 %Allylaiuminum compounds were shown to undergo allylic rearrangement,‘6.‘7.‘8during which cis-trans isomerization could take place.

We could not detect any products arising from 22. Apparently the preferred charge localization on a primary rather than a secondary C-atom and the greater steric accessibility to the olefin attack in the dimerization step tips the balance in favor of 19. The effect of substitution on the reaction mode is in consonance with this general scheme. The most powerful electron-donating anisyl group favors the formation of the carbon cationic moiety 21, which polymerizes in high yield. In the case of 5 and 6, it is the bulky Spiro structure which sterically precludes the dimerization, thus terminating the reaction at the monomeric stage (12 and 13). The non-occurrance of dimerization in 7 and 8 is most likely due to electronic effects, namely the olefinic bond is too weakly polar for further addition. The. observed cis stereospecificity can he explained eitht% in terms of the geometry of the transition-state 18, or as the result of a thermodinamically-controlled process.‘3 The influence of the methyl and cyclopropyl is apparently intermediary between the anisyl and the p-chlorophenyl substituents, enhancing dimerization (to 16 and 17) but not polymerization. Precedents to formation of cis-trans mixtures in homoallylic rearrangements of these systems have been recorded.” -AL

Yields calculations are based on the amount of vinylcydopropane compound present in the preparatively isolated materials. IR spectra were obtained neat with Perkin-Elmer 237 spectrophotometer. NMR spectra were determined in CCL solutions with TMS as internal standard on a Jeol JMN-C-6OH spec-

995

AK&-induced reactions of vinylcyclopropanes

+

Et20 _

AlC12 dl

R R

[

c

Awl2

1 12-15 --

A1C12

Cl dimer

If

16 17 -*-

AlC12 Cl [Jr

Scheme 2 trometer; the chemical shifts are reported in r values and 1 couplings in Hz units. MS were taken on a Varian MAT CH-5 spectrometer. GLC were carried on a Varian-Aerograph A-90P3 gas-chromatograph (TCD) with a 6 ft X l/4 in., 10% SE-30 on, Chromosorb W. column at appropriate temperatures in the IOO180”range and He flow rate of 20-50 ml/min. The starting materials were prepared by literature procedures-5 and 6.19 1 1O.2’ . 11.” . 7. 8 and 9.” monoetherate’ General procedure. Aluminum chloride (5 mmole) was distilled (IOO-lOS”/O.S mm) into a round-bottomed flask equipped with a magnetic stirring bar, and the flask was sealed with a rubber septum under Na. 8 ml of dry ether were added by injection, followed by a soln of the vinylcyclopropane compound (5 mmole) in 2 ml dry ether. The mixture was stirred at room temp. until the substrate was consumed (20-3Omin, determined by GLC). The mixture was then poured into excess Na#ZOsaq., the organic layer separated and the aqueous phase extracted with additional ether. The combined etheral soln was washed with water and dried over MgSOd. The solvent was removed in vacuum and the product separated by GLC from the residue. 1 - Methyl - 2 - (2 - chloroethyl) - 1 - cyclohexene, 12, yield: 62%; IR: 740 (C-Cl) cm-‘. NMR: 7 8.60-7.98(8H, m), 8.38 (3H, s, Cl&), 7.60 (2H, t, J 7.5. CH&HaCI), 6.58 (2H, t, J 7.5, C&Cl); MS: m/e 158, 160 (100:33, M+), 109 (M-CH,CI); 95 (MCH$ZHaCI,base peak); 81 (M-CHICI- C2H4,retro Diels-Alder); 67 (M - CHaCH,CI- C2H4,retro Diels-Alder). (Found: C, 67.98, H, 9.49, Cl, 22.30.Calc. for CsH&I: C, 68.14, H, 9.46, Cl, 22.40%). 3 - (2 - Chloroethyl) - 2 - methyl - I,1 - ethano - 2 - cyclohexene, 13, yield: 76%; IR: 3070, 1010(cyclopropane), 720 (C-Cl) cm-‘; NMR: r 9.48 (4H, AiB;, cyclopropane), 8.70 (3H, s, CHs), 8.65-8.10 (4H, m), 8.10-7.75(2H, m, cyclic allylic), 7.60 (2H, t, J 8.0, CHaCHsCI),6.60 (2H, t, J 8.0, C&Cl), MS: m/e 184, 186 (100:33, M’), I35 (M - CHxCI),121(M - CHaCHaCI),base peak), 107(M - CHzCl- CrH,, retro Diels-Alder), 93 (M - CHsCHaCIC2H4,retro Diels-Alder). (Found: C, 71.31, H, 9.27, Cl, 19.28. Calc. for C,,H,,CI: C. 71.53, H, 9.28, Cl, 19.20%). cis - 2 - Phenyl - 5 - chloro - 2 - penMe,*’ 14, yield: 66%; JR: 735 (C-Cl) cm-‘. NMR: r 7.95 (3H, s, CH,), 7.37 (2H, q. J 7.0,

CHsCH$I), 6.47 (2H, t, J 7.0, C&Cl), 4.32 (IH, tq, Ju.cu2 7.0, J “Ct.,31.5, vinyl), 2.82 (5H, broad single band); MS: m/e 180, I82 (100:33, M’), 131(M - CH#.ZI),91 (tropilium, base peak). cis - 2 - (4 - Chlorophenyl) - 5 - chforo - 2 - pentene,% 15, yield: 57%: IR: 730 (C-Cl) cm-‘, NMR: r 7.97 (3H, s, C&), 7.38 (2H, q, J 7.0, CI&CH#.ZI),6.47 (2H, t, J 7.Q,C&Cl), 4.38 (IH, tq, Ja,cu* 7.0, JH.CH,I 59vinyl), 2.80 (4H, broad single band). cis - trans - 2,4 - Dimethyl - 2 - cyclopropyl - 7 - chloro - 4 heptene, 16, yield: 68%; IR: 3080, 1015(cyclopropane), 720 (CCl) cm-‘; NMR: r 9.95-9.65 (4H, m, cyclopropane C&), 9.609.00 (IH, m, cyclopropane CH), 9.28(s)+9.23(s) (4: 1, 6H, CHs), 8.28(s)t 8.19(s) (4: I, 3H, allylic CHs), 8.03(s)+7.95(s) (4: I, 2H, isolated CH,), 7.54 (2H, diffuse q. J 7.0, CJ&CHaCI),6.590)t 6.56(t) (1:4, 2H, J 7.0, C&Cl), 4.88 (IH, diffuse t, J 7.0, vinyl). (Found: C, 71.83, H, 10.70, Cl, 17.20. Calc. for &H2,Cl: C, 72.00,H, 10.50,Cl, 17.50%). cis-trans - 2,2,4 - Tricyclopropyl - 7 - chloro - 4 - heptene, 17, yield: 76%; IR: 3080, IO15 (cyclopropane), 715 (C-Cl) cm-‘; NMR: r 9.96-8.33(15H, m, cyclopropane), 9.50(s)t 9.45(s) (4:7, 3H, C&), 8.10(s)+7.78(s) (4:7, 2H, isolated CH*), 7.50(q)t 7.32(q) (7:4, 2H, J 7.0, CI$CH2CI), 6.600)+6.47(t) (7:4, 2H, J 7.0, C&Cl), 4.93(t)t 4.63(t) (7:4, IH, J 7.0, vinyl): MS: m/e 252, 254 (100:33, M’), 109 ( &CHs)-Q

, base peak). (Found: C,

75.87, H, 10.20,Cl, 13.93.Calc. for C,,HzCl: C, 76.01, H, 9.97, Cl, 14.02%).

‘T. Takahashi, I. Yamashita and T. Miyakawa, Bull. Chem. Sot. Japan 37, 131(1964). *T. Takahashi and I. Yamashita, 1. Polymer Sci. Part B, 3, 251 (1%5). 9. Takahashi, Ibid. Part A-l, 6,403, 3327(1968). ‘A. D. Ketley, A. J. Berlin and L. P. Fisher, Ibid. Part A-l, 5, 227 (1%7). ‘A. D. Ketley, Chem. Abstr. 66, P 66026g(1%7). 6C. P. Pinazzi, A. Pleurdeau and J. C. Brosse, Makromol. Chem. 142,259 (1971). ‘A. R. Volchek, V. M. Zuiin, A. S. Shashkov, 0. M. Nefedov

996

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YOVELL

and A. Ivashenko, Vysokomol. Soedin., Ser. A 15,2258 (1973); Chem. Abstr. 80,4857h (1974). ‘L. I. Belenkii, S. Z. Taits and Ya.L. Goldfarh, Do/d. Akad. Nauk S.S.S.R. 139, 1356(1961);Chem. Abstr. 56,450f (!%2). 9D. H. Jenkinbon and D. C. Pepper, Proc! Roy. Sot. 263A, 82 (!%I). ‘OH. Haraguchi and S. Fujiwara, 1. Phys. Chem. 73, 3467 (!%9). “G. A. Olah, Friedel-Crofts and Related Reactions (Edited by G. A. Olah), Vol. I, p. 242. Interscience, London, (!%3). “S. Sarel and R. Ben-Shoshan, Tetrahedron Letters 1035 (!%5). “S. Sarel, J. Yovell and M. Sarel-Imber, Angew. Chem. Int. Ed. 7.577 (I%&?)and refs cited. $. Schmerling, Ind. Eng. Chem. 40,2072 (1948). 15Ref.11,p. 214-S. 16H. Lehmkuhl and K. Ziegler, Houben-Weyl, Methoden der

et cd.

Organischen

Chemie, Vol. XIII/I, p. 144. Thieme-Verlag, Stuttgart, (1970). “H. Lehmkuhl and D. Reinehr, J. Organometal. Chem. 23, C2S (1970). ‘sJ. J. Eisch and G. R. Husk, Ibid. 4,415 (!%5). 19S.Sarel, A. Felzenstein and J. Yovell, L Chem. Sot. C/tern. Comm. 859 (1973). ?S Sarel, E. Breuer, S. Ertag and R. Solomon, Israel 1. Chem. 1, 451 (1963). 2’R V Volkenburgh, K. W. Greenlee, J. M. Derfer and C. E. Biook, J. Am. Gem. Sot. 71, 172(1949). **I. A. D’yakonov and 1. M. Stroiman, Zh. Obshch. Khim. 33, 4019(!%3); Chem. Abstr. 60,9!59p, (1964). 23T A. Favorskaya and Sh. A. Frid;nan, J. Gen. Chem. u), 613 (1950). “P. A. J. Janssen, Chem. Abstr. 65, P8925b (1966).